Unfortunately, if the Flash 26 installer didn't "clean up" the old version, you have to do it yourself. Since the Flash plugin is stored in a shared folder, this needs to be done outside of Firefox. ''Official Method'' Adobe has released an uninstaller that will remove ALL Flash from your system, and then you can reinstall just the latest version. This article has a link to the uninstaller: https://helpx.adobe.com/flash-player/kb/uninstall-flash-player-windows.html ''Unofficial Method'' If you only want to remove one file -- the old Flash plugin DLL file -- you can delete it by hand. To learn the location, type or paste '''about:plugins''' in the address bar and press Enter to load it. On that page, search for ''npswf'' which is part of the file name for the Flash plugin. You should find two versions, and the one with 23 in it is the one you want to track down and remove. On Windows 7, 64-bit, 32-bit Firefox usually uses this folder for Flash: C:\Windows\SysWOW64\Macromed\Flash When you look in that folder, be careful to only remove the file listed on the about:plugins page for the old version, since other applications may use the other old files. But don't stress out too much about messing up, you can always use the Official Method to clean up and reinstall. Does that help at all?